1. The problem statement, all variables and given/known data Excuse my english, it is not my first language. A bookcase has the weight 1500N and is standing at a horizontal floor. The friction force between the floor and the shelf is 600N. The shelf's height is 1,8mand it is 2m wide. The shelf stands on four feet each 0,01m from the edge. The masscentre is located at the middle of the shelf. A person pulls at the top of one of the shelf's edges. The force creates an angle v with the shelf's side. I have to form an expression for when the shelf starts gliding, as a function of the angle v. I will add a file with a pictur that explains the situation. 2. Relevant equations torque, T=Fxr Friction, Ff=uN 3. The attempt at a solution I have calculated the force needed to tip the shelf at v=90degrees: 13500N. Also the force needed to make the shelf start gliding when v=0(paralell)=600N. The force needed to tip the shelf at v=0 is 750N I have no idea how to form the function.